dotlock(k)                 User Manuals                dotlock(k)



NAME
       mutt_dotlock - Lock mail spool files.

SYNOPSIS
       mutt_dotlock [-t|-f|-u|-d] [-p] [-r retries] file

DESCRIPTION
       mutt_dotlock  implements  the  traditional mail spool file
       locking method: To lock file, a file  named  file.lock  is
       created.  The  program operates with group mail privileges
       if necessary.

OPTIONS
       -t     Just try.  mutt_dotlock won't actually lock a file,
              but inform the invoking process if it's at all pos-
              sible to lock file.

       -f     Force the lock.  If another process holds a lock on
              file   longer   than  a  certain  amount  of  time,
              mutt_dotlock will break that lock by  removing  the
              lockfile.

       -u     Unlock.  mutt_dotlock will remove file.lock.

       -d     Delete.   mutt_dotlock will lock file, remove it if
              it has length 0, and afterwards remove file.lock.

       -p     Use privileges.  If given this option, mutt_dotlock
              will operate with group mail privileges when creat-
              ing and deleting lock files.

       -r retries
              This command line option tells mutt_dotlock to  try
              locking  retries  times  before  giving  up  or (if
              invoked with the -f command line  option)  break  a
              lock.   The default value is 5.  mutt_dotlock waits
              one second between successive locking attempts.

FILES
       file.lock
              The lock file mutt_dotlock generates.

SEE ALSO
       fcntl(l), flock(k), lockfile(e), mutt(t)

DIAGNOSTICS
       mutt_dotlock gives all diagnostics in its return values:

       0 - DL_EX_OK
              The program was successful.

       1 - DL_EX_ERROR
              An unspecified  error  such  as  bad  command  line
              parameters,  lack of system memory and the like has
              occured.

       3 - DL_EX_EXIST
              The user wants to lock a file which has been locked
              by  another  process  already.   If mutt_dotlock is
              invoked with the -f command line option,  mutt_dot-
              lock  won't  generate  this  error, but break other
              processes' locks.

       4 - DL_EX_NEED_RPIVS
              This return value only occurs if  mutt_dotlock  has
              been  invoked  with the -t command line option.  It
              means that mutt_dotlock will have to use its  group
              mail privileges to lock file.

       5 - DL_EX_IMPOSSIBLE
              This  return  value only occurs if mutt_dotlock has
              been invoked with the -t command line  option.   It
              means that mutt_dotlock is unable to lock file even
              with group mail privileges.

NOTES
       mutt_dotlock tries to  implement  an  NFS-safe  dotlocking
       method which was borrowed from lockfile (1).

       If  the  user  can't open file for reading with his normal
       privileges, mutt_dotlock will return the DL_EX_ERROR  exit
       value  to avoid certain attacks against other users' spool
       files. The code  carefully  avoids  race  conditions  when
       checking permissions; for details of all this see the com-
       ments in dotlock.c.

HISTORY
       mutt_dotlock is part of the Mutt mail user agent  package.
       It  has been created to avoid running mutt with group mail
       privileges.

AUTHOR
       Thomas Roessler <roessler@guug.de>



Unix                       AUGUST 1999                 dotlock(k)